US3481294A

US3481294A - Anchored riser pipe mooring system for drilling vessel

Info

Publication number: US3481294A
Application number: US766670A
Authority: US
Inventors: Renic P Vincent
Original assignee: Pan American Petroleum Corp
Current assignee: Pan American Petroleum Corp
Priority date: 1968-09-20
Filing date: 1968-09-20
Publication date: 1969-12-02
Anticipated expiration: 1986-12-02

Description

Dec. 2, 1969 R. P. VINCENT 3,481,294

ANGHORED RISER PIPE MOORING SYSTEM FOR DRILLING VESSEL Original Filed June 26, 1967 2 Sheets-Sheet 1 RENIC P. VINCENT INVENTOR.

BYfdZ (2 ATTORNEY.

Dec. 2, 1969 R. P. VINCENT 3,481,294

ANCHORED RISER PIPE MOORING SYSTEM FOR DRILLING VESSEL Original Filed June 26, 1967 2 Sheets-Sheet 2 I I RENIC I? VINCENT INVENTOR.

ATTORNEY.

United States Patent 3,481,294 ANCHORED RISER PIPE MOORING SYSTEM FOR DRILLING VESSEL Renic P. Vincent, Tulsa, Okla., assignor to Pan American Petroleum Corporation, Tulsa, Okla., a corporation of Delaware Continuation of application Ser. No. 648,580, June 26, 1967. This application Sept. 20, 1968, Ser. No. 766,670 Int. Cl. B63b 35/44 U.S. Cl. 114--.5 12 Claims ABSTRACT OF THE DISCLOSURE This describes an anchoring system for a drilling vessel. A large diameter vertical pipe, i.e., a riser pipe, is buoyantly supported in a body of water by a chamber at the top and by a pad at the bottom. The riser pipe is provided with an anchoring system and the chamber contains anchor winches whose cables are connected to anchors in the ocean floor at points surrounding the riser pipe. The anchoring system is made sufliciently strong to moor not only the riser pipe but also a drilling ship. The drilling ship is connected to the vertical pipe by a unique system so that the ship can weathervane about the pipe. This includes a band rotatably mounted about the vertical pipe and arms connecting the ship to ball joint type pivots on the band. The cantilever drilling deck is supported from the ship above the vertical pipe. The vertical pipe is exterior of the ship and in case of a sudden storm, the ship can be disconnected therefrom quickly.

This application is a continuation of co-pending application 648,580, entitled Anchored Riser Pipe Mooring System for Drilling Vessel, filed June 26, 1967, Renic P. Vincent, inventor and now abandoned.

This invention relates to the mooring or anchoring of a vessel floating on a body of water through which it is desired to drill a well.

BACKGROUND OF THE INVENTION One of the areas in which oil is very actively being searched for is the so-called offshore areas, such as in the continental shelf in the Gulf of Mexico. The depth of water in these offshore areas may range from a few feet to a thousand or more feet in depth. In the shallower water, e.g., up to about 200 feet or so, it has usually been the practice to conduct drilling operations from a fixed platform, that is, a platform supported by steel framework from the underwater bottom. Sometimes this framework takes the shape of a submersible vessel which can be partially flooded so that its legs or bottom rest on the underwater bottom. Other means include permanent platforms constructed on the top of piles which have been driven in the ocean floor and extended above the surface of the Water.

As the water depths become excessive, it becomes more and more diflicult to construct such fixed platforms. It has therefore become the practice of drilling wells in deeper water from floating platforms or floating drilling vessels. One of the main problems confronting drilling from a floating structure are those of maintaining the structure in a fixed position under the influence of wind, waves, current and tide action.

Frequently, anchor lines extending out from the floating vessel are utilized to restrain the motion of the ship. Various patents and other prior art have issued or been published showing deep-water mooring systems. While these various systems have been quite helpful, a common problem lay in the difliculty in mooring the ship with respect to the wind and waves. It is normally desirable to point the bow of the ship into the wind to maintain roll of the ship at a minimum. With a given lateral anchortype of mooring system, the adjusting of the ships direction of orientation is normally limited to something less than Efforts have been made to eliminate or reduce this difliculty. One such effort is described in U.S. Patent 3,279,404. In that patent a mooring member is carried by the vessel within the vertical well through which drilling is conducted. The mooring members carries connections for anchoring means which extend through anchors set in the ocean floor. The mooring members is mounted such that it permits relative rotation between the member and the vessel so that the vessel may be oriented 360 about the member. This system requires that the ship be connected through the mooring member and a plurality of anchors.

Another type of mooring system is disclosed in U.S. Patent 2,699,321 in which a floating oil storage vessel is provided with a vertical well. A rigid shaft extends through this vertical Well into anchor engagement with the submerged bottom. The vessel may rotate about the vertical shaft and may slide up and down with respect thereto. There, the vertical structure must be made quite rigid and strong to withstand storm actions as no means are provided for quick release of the ship from the vertical structure in case of a sudden storm. In fact, the patentee contemplates such a system will provide a protected harbor in the lee of the vessel for the accommodation of vessels associated with drilling operations, and as a harbor of refuge for distressed craft in stormy weather. The system of Patent 2,699,321 has the further ditficulty of making the vertical structure strong enough to withstand the high stresses induced by yawl of the ship.

SUMMARY OF THE INVENTION Briefly, this is an invention concerning a mooring system for a drilling vessel floating on a body of water. A vertical riser pipe is placed at the proposed drilling location and is supported at the lower end from the ocean floor by pads or other means and preferably at the upper end by a buoyant chamber to maintain the pipe in tension. Means are provided for connecting the riser pipe to the drilling vessel. These means are such as to provide not only for rotation of the ship about the riser pipe but also so that the ship may pivot vertically with respect to the longitudinal axis of the riser pipe. The riser pipe is exterior of the ship and means are provided for rapid disconnecting of the ship therefrom. If the ship must make a sudden departure due to an emergency, there may still be pipe suspended in the riser pipe. Means are provided to support such pipe within the riser pipe after the ship has left the drilling site. A cantilever drilling deck extends over the riser pipe when connected to the ship.

The anchoring system of the riser pipe is sufliciently strong to anchor the drilling vessel in ordinary weather. If the weather becomes bad, the ship disconnects from the riser pipe and rides the storm out at sea or proceeds to a safe harbor. The anchoring system which is strong enough to hold the drilling vessel during normal weather is ordinarily able to maintain the riser pipe without the drilling vessel connected thereto in very great storms. After the storm has subsided, the drilling vessel can again be anchored to the riser pipe.

DESCRIPTION OF THE DRAWINGS Various objects and a betterunderstandingcf the invention can be had when considering the above described drawings and the following description of the best mode contemplated for carrying out the invention.

Attention is first directed to FIGURE 1 which shows a ship having a cantilever drilling deck 12 extending above vertical pipe 14. Details of the anchoring of this pipe 14 will be discussed hereinafter. The only anchoring which ship 10 has is through its connection to vertical pipe 14. This connection, too, will be described in detail.

Vertical pipe 14 is supported from the bottom 17 of the body of water 18 by pads 20, for example. The pipe 14 can extend into the bottom 17 and, if desired, be cemented at 19 therein. The size of pipe 14 is large enough so that drilling operations can be conducted therethrough. Typical diameters for pipe 14 are in the range of from 30 to 42 inches. The pipe 14 may extend into the ground or bottom 17 for any selected distance, such as a typical distance being about 20 to feet.

Pipe 14 is held in tension by a buoyant chamber 22 which is attached to the pipe at the upper end thereof. This chamber 22 should be large enough to house anchor winches 24 therein and to permit entry for service by workmen. Buoyant chamber 22 to have buoyancy is mounted at least partially beneath the surface of the body of water. It is preferred that the upper end be above the water to facilitate entry (at least at low tide). Chamber 22 is preferably kept closed to prevent entry of water thereinto. The size of chamber 22 should be Sufi'lClCnt to have adequate displacement to place pipe 14 in tension, preferably throughout the entire length of the riser pipe. Pipe 14 is anchored through anchor lines 26 of anchor winches 24 to anchors 28 which are secured to the floor of the body of water. There are preferably at least four such anchors equally spaced about pipe 14. Anchor lines 26 can pass through the walls of chamber 22 in sealed relationship, or the lines can enter the chamber above the water line.

Anchor winches 24 are preferably electrically motor driven with power source on ship 10 so that they can be controlled readily by workmen on the ship. The anchor system, together with pipe 14, must be of sufficient strength to anchor vessel 10 during normal drilling operations. It need not be strong enough to hold vessel 10 in event of storms of the magnitude to disrupt drilling operations, but must be strong enough to maintain the riser and attached buoyant chamber in osition during the most severe storms for which the system is designed. The reason for this is that the ship will be disconnected from the pipe 14 upon the approach of a storm and seek shelter in a harbor or ride the storm out at sea. When the storm subsides, the vessel will again be connected to the pipe and drilling operations will again begin. If the anchoring system is strong enough to anchor the ship, then without the ship it can usually ride out most of the severe storms.

Attention is now directed toward means for connecting ship 10 to buoyancy chamber 22 which is fixed to vertical pipe 14. The two are connected by elongated rods or members 30 as better shown in FIGURES 2, 2A and 3. These are connected by horizontal pivots 32 at one end of the ship and at the other end through a ball and socket joint 33 to band 36. Horizontal pins 32 are spaced in opening or V-shaped wells 38 which have been provided in the hull of the ship. This permits the ship to yawl, i.e., the stern moves up while the bow moves down, or vice versa, without causing undue stress or strain upon pipe 14.

Ball and socket joint 33 includes socket member 34 which is adapted to receive ball member 35 which is supported by arm 35A from band 36. Band 36 is mounted about circumferential member 41 which is attached about buoyancy chamber 22 in a fixed relationship. Band 36 is rotatably supported from member 41 by ball bearings 42. This permits ship 10 to rotate about pipe 14 so that 4 it can always weathervane. Ordinarily, permitting the ship to weathervane will keep it from rolling. However, if the ship does roll, it can do so without twisting the arms 30 v as ball and joint 33 will permit such movement. Ball joints 33 are shown as connecting arms 30 to band 36. If preferred, the ball joint assembly could connect the arm 30 to the ship. Or alternatively, the ball joint 33 could be at each end of rod 30.

As can be seen in FIGURES 1 and 2, drill pipe 44 extends through pipe 14 for performing drilling operations. This drill string has the conventional slip joint 46. Drilling mud is circulated down through drill pipe 44 by conventional means and returned up the annulus between the drill pipe and pipe 14 or other strings of pipe which may be hung in pipe 14 to reduce the size of the annulus. The mud return is taken from the annulus 15 by conduit 48 having valve 49. Conduit 48 leads to the mud pit (not shown) on vessel 10. Deck 12 extends over the riser pipe 44 and is provided with a derrick 50 and other equipment for drilling boreholes in the bed of the body of water.

As mentioned above, sometimes it is desirable to disconnect the ship from the anchor mechanism upon rather short notice. This can conveniently be done with this system. As shown in FIGURE 2, socket 34 is provided with explosive chamber 37 in which an explosive mixture 39 is placed. It is provided with a firing charge and firing circuit 39A. Means for firing an explosive mixture is well known; therefore, no details of such means are shown. When it is desired to disconnect the Ship from the riser pipe, all that is necessary to do is to detonate the explosive 39 and socket 34 is disintegrated, thus separating arm 30 from band 36. Then the ship can immediately leave. By replacing the end of arm 30, the ship can readily be reattached to the anchoring means. It will be noted that pipe 14 is exterior of any part of ship 10. The ship can therefore be parted from pipe 14 without losing any time in removing any part of shaft or pipe 14. In fact, it is an object to leave pipe 14 and its buoy 22 intact. Further, if there has not been adequate time of warning to remove the drill string, the drill string can be left suspended in pipe 14. Means for providing this are shown in FIGURE 1. Shown there above buoyant chamber 22 are slip and bowl assembly 60 which is mounted above blowout preventer assembly 62 which is attached to the upper end of pipe 14. If it is desired to leave the drill pipe 44 standing in the hole, all that is necessary to do is actuate slip and bowl assembly 60, disconnect the drill pipe above the slip and bowl assembly, actuate blowout preventer 62 and sever connection between arm 30 and ball 35 by firing explosive 39. Re-connection of the ship and re-connecting to the drill pipe are simple procedures.

If the length of arm 30 is 40 feet and the ship rises and lowers 15 feet, the angle alpha which the rod 30 makes with the horizon is 15". This is indeed a tolerable amount.

While the above embodiments of the invention have been described with considerable detail, it is to be understood that various modifications of the device can be made without departing from the scope or spirit of the invention.

I claim:

1. A mooring system for a drilling vessel floating on a body of water used for drilling boreholes in the bottom of said body, which comprises:

(a) a vertical pipe means forming a passage through which drilling equipment can be moved for operation in said borehole;

(b) means anchoring the base of said' vertical pipe means to the floor of said body of water;

7 (c) connecting means for connecting said vessel to said vertical pipe means, said connecting means including a pivotal connection therebetween such that the ship can roll and move vertically and rotationally about said vertical pipe means, the only anchoring of said vessel to the bottom of said body of water is through said vertical pipe means.

2. A system as defined in claim 1 wherein said means anchoring said pipe means includes lines connected at one end to the pipe means and means connecting the other end of said lines to the ocean floor at points removed from the base of said pipe means.

3. A system as defined in claim 1 including tensioning means to maintain said vertical pipe means in tension.

4. A system as defined in claim 3 in which said tensioning means is a buoy member connected to and surrounding an upper end portion of said vertical pipe means.

5. A system as defined in claim 4 including anchor winches in said buoy member, anchors in the floor of the body of water, and lines connecting such anchors to said anchor winches.

'6. A system as defined in claim 1 in which said connecting means contains an explosive.

7. A system as defined in claim 1 in which said drilling vessel has a cantilever drilling deck with a drilling derrick thereon positioned above said vertical pipe means such that drilling can be carried out through said vertical pipe means.

8. A system as defined in claim 1 in which said connecting means includes a band mounted about the exterior of said pipe in a rotatable nonlongitudinal relationship with pivots extending outwardly from said band; horizontal pivots supported by said vessel; and a rigid member extending from the pivots on said band to said horizontal pivots supported by said vessel.

9. A mooring system for offshore drilling operation which comprises:

a vertical pipe through which drilling can be effected;

means securing said pipe to the floor of the body of Water;

a drilling vessel having a cantilever drilling deck extending outwardly from one end thereof, said deck extending over said vertical pipe so that drilling operations can be conducted therethrough;

connecting means exterior said vessel for connecting said vessel to said vertical pipe including first means permitting rotational movement of said vessel about the longitudinal axis of said riser pipe and second means pivotally connecting said vessel to horizontally oriented pivot points positioned in a plane perpendicular to said longitudinal axis of said riser pipe, the only anchoring of said vessels to the said floor of the body of water is through said vertical pipe.

10. A mooring system for a drilling vessel floating 0:1 21 body of water used for drilling boreholes in the bottom of said body, which comprises:

a vertical pipe forming a passage from above the surface of said body to said borehole and through which drilling equipment can be moved;

means anchoring the base of said pipe to the floor of said body of Water;

buoyant means connected to the top of said vertical pipe for applying tension thereto;

connecting means for connecting said vessel to said pipe, said connecting means including:

(i) a rigid elongated member;

(ii) a rotating member rotatably mounted about the upper end of said vertical pipe;

(iii) first pivotal connection between said elongated member and said rotating member;

(iv) second pivotal connecting means between said elongated member and said vessel.

11. A system as defined in claim 10 in which said first pivotal connecting means includes a ball and joint connection and an explosive charge in said elongated member adjacent said ball and joint connection.

12. A mooring system for use with a drilling vessel floating on a body of water used for drilling boreholes in the bottom of said body, which comprises:

means anchoring the base of said pipe to the floor of said body of water;

a band mounted about said buoyant means in a rotational relationship therewith said band having a pivot point thereon.

References Cited UNITED STATES PATENTS 3,015,360 l/1962 Stratton 7 X 3,189,093 6/1965 DeVries 114-05 X 3,296,995 1/ 196 7 Van Der Linde.

3,361,200 l/l968 Chambers 1660.6

TRYGVE M. BLIX, Primary Examiner US. Cl. X.R.